The method of developing a latent image formed on a photoconductive surface by means of electrophoretic transfer of liquid toner is well known in the art. In this method, charged particles suspended in a non-polar insulating carrier liquid migrate under the influence of an electrostatic field and concentrate in an image forming configuration upon relatively charged or discharged areas of a photoconductive surface. The developed image is then transferred to a substrate, such as paper, either directly or by means of one or more intermediate transfer members.
In U.S. Pat. No. 4,504,138 a different method for the developing of a latent image is described. This patent describes applying a thin viscous high density layer of toner particles on the circumferential surface of a roller and bringing the layer so formed to the photoconductive surface. Transfer of selected portions of the toner layer onto the photoconductive surface then occurs due to the electric field induced by the latent image.
In Canadian Patent 990589, a method of developing electrostatic images is described which involves producing a film of liquid toner on a first applicator and bringing the applicator in contact with the final substrate which carries a latent image, thereby to develop the image. A second applicator bearing a layer of carrier liquid is then brought into contact with the substrate to remove background deposits and to squeegee out excess liquid. The film of liquid toner described in Canadian Patent 990589 has between 2-4 per cent of toner concentrate dispersed within the carrier liquid.
A latent image development apparatus described in U.S. Pat. No. 4,327,664 includes a porous, resilient sponge, development roller which is circumferentially surrounded by a net of fine mesh size. The developer roller is urged against the latent image carrying surface of a drum and liquid toner, which is carried in the roller is squeezed out of the compressed sponge through the fine net. Toner particles which are contained in the liquid toner are selectively deposited, by electrophoresis, onto the surface of the drum to form an image.
U.S. Pat. No. 4,400,079 describes a liquid toner development system for developing a latent image on a photoreceptor that uses a non-contacting developer roller. The development roller surface may move in the same direction as the photoreceptor surface or in the opposite direction.
Most of the above mentioned apparatus, as well as many other techniques which are known in the art, are concerned with producing a layer of toner on the surface of a developing roller and transferring the entire thickness of the layer to image of a latent image on an image bearing substrate. For such systems, the uniformity of the layer thickness is important, since this thickness determines the density of the image. Normally, it is very difficult to control the uniformity of the developing layer even by expensive and complicated means, especially when the layer thickness is generally a function of the previous imaging history of the apparatus.